This invention generally relates to gas metal arc welding (GMAW) and flux core arc welding (FCAW). In particular, the invention relates to wire feeding guns.
Wire feeding guns must perform several different functions in order for successful welding to occur. Those functions include directing the weld wire to the workpiece, conducting electric power to the weld wire, and shielding the welding arc from atmospheric air. In addition to the foregoing basic requirements, it is highly desirable that the weld wire be fed to the workpiece at an adjustable rate that suits the particular welding operation at hand. For maximum productivity, it is also necessary that the gun be very comfortable for the operator to maneuver as he directs the weld wire to the workpiece.
To satisfy the foregoing requirements, the wire feeding gun is connected by a long flexible cable to a wire feeder, which is wired to a welding machine. The wire feeder supplies the weld wire, electric power, cooling fluid, and shielding gas through the cable to the gun. In some instances, the cable may be as long as 50 feet.
In a typical wire feeding gun arrangement, there is a head tube on the end of the handle opposite the flexible cable. A diffuser is joined to the free end of the head tube. A contact tip is connected to the diffuser. The weld wire is guided by a liner (i.e., a tube), placed inside the head tube, that extends from the handle to the diffuser. From the diffuser, the weld wire passes through an axial hole in the contact tip, from which it emerges under the impetus of the feed mechanism.
In gas-shielded applications, it is vital that the gas adequately shield the welding arc from the ambient atmosphere. For that purpose, gas is supplied to the wire feeding gun from the wire feeder through the flexible cable. The gas is directed through the head tube to the interior of the diffuser. The gas flows from the diffuser to a nozzle that surrounds the contact tip. The gas then flows out the nozzle and surrounds the contact tip and the weld wire emerging from the contact tip. The gas thus shields the weld wire and the welding arc from the ambient atmosphere.
U.S. Pat. No. 6,225,599 discloses a MIG welding gun wherein the weld wire passes through the interior of a liner having a frusto-conical chamfer surface at its downstream end and then through the bore of a diffuser having a frusto-conical surface of the same geometry as the liner chamfer. The liner chamfer abuts the diffuser frusto-conical surface to locate the liner relative to the diffuser. The apex end of the diffuser frusto-conical locating surface terminates in a short modified cylindrical surface. From the cylindrical surface, the diffuser bore opens at a radial surface to receive the outer diameter of the contact tip. The contact tip has an axial hole through which the weld wire passes.
The diffuser disclosed in U.S. Pat. No. 6,225,599 has a short modified cylindrical surface between the diffuser locating surface and an enlarged inner diameter. An angled surface connects the enlarged inner diameter with the modified cylindrical surface. The diffuser inner diameter cooperates with the liner outer diameter to form a relatively large annular chamber. One or more radial holes extend through the diffuser wall from the inner diameter to the diffuser outer surface. Upstream of the annular chamber, the diffuser has a smaller inner diameter that surrounds the liner and cooperates with it to form a relatively long passage. Inert gas under a pressure greater than atmospheric pressure flows down this passage to the annular chamber, out the radial holes and into the space outside the contact tip and inside the nozzle. From this space, the inert gas flows out the open end of the nozzle to surround the welding arc.
To prevent atmospheric air present in the interior of the liner from flowing through the axial hole in the contact tip to the arc, U.S. Pat. No. 6,225,599 discloses the formation of an inert gas seal that blocks atmospheric air in the liner from entering the contact tip hole. This is achieved by bleeding some of the inert gas in the diffuser annular chamber through an axial passage that communicates with the interior of the liner at the tip of the latter. The pressure of the inert gas in the liner interior blocks atmospheric air in the liner interior upstream of the gas seal from flowing downstream into the contact tip hole. In one disclosed embodiment, the gas seal comprises a sealing space between the downstream end of the liner and the upstream end of the contact tip. The weld wire is unsupported within this sealing space. The gas seal bleeds inert gas from the diffuser annular chamber through a passage to the liner interior by way of the sealing space. The passage of the gas seal is in the form of at least one and preferably more (e.g., three) slots formed in the diffuser between the annular chamber and the sealing space. Other than through these slots, the contact of the liner chamfer with the diffuser locating surface prevents communication between the annular chamber and the sealing space. In addition to flowing out the radial holes, some of the inert gas in the diffuser bleeds through the slots to the sealing space and then, due to the higher than atmospheric pressure, tends to flow upstream into the interior of the liner. That action blocks any atmospheric air in the liner interior from reaching the sealing space. Some of the inert gas will also flow downstream from the sealing space into the contact tip hole, thereby providing an even more effective blockage to any air that might reach the sealing space. The result is that the welds of the workpiece are substantially free from sooty deposits.
The U.S. Pat. No. 6,225,599 teaches the concept of creating a direct route for the shielding gas to get past the downstream end of the liner and into the contact tip hole, thereby improving shielding performance. However, there is a need for an improved design that replicates the foregoing shielding performance benefits, but is less complex and less costly to manufacture.